CA2010789C

CA2010789C - Siloxane resins and method for making them

Info

Publication number: CA2010789C
Application number: CA002010789A
Authority: CA
Inventors: Derek W. Butler
Original assignee: Dow Corning Ltd
Current assignee: Dow Silicones UK Ltd
Priority date: 1989-03-22
Filing date: 1990-02-23
Publication date: 1999-01-12
Anticipated expiration: 2010-02-23
Also published as: DE69011162D1; DE69011162T2; US5109095A; EP0389137A3; EP0389137A2; ES2057373T3; CA2010789A1; JPH02281040A; GB8906627D0; EP0389137B1

Abstract

Liquid organosiloxane MTQ resins of the general formula [M x T y Q z]n wherein M denotes a monofunctional, T a trifunctional and Q denotes a tetrafunctional siloxane unit is characterised by the fact that n has an average value of from 4 to 14, x+y is not less than z and not more than 2 z and x/y has a value of from 2/1 to 9/1. The resin molecule has at least one reactive substituent as defined and can be made by a method comprising (I) adding together a tetraalkoxysilane, a monoorganosilane and a triorganosilane or hexaorganodisiloxane in an acidified aqueous medium provided the tetraalkoxysilane is not added to the aqueous medium prior to the other components, (II) allowing the components to react together in said aqueous medium and, optionally (III) further reacting the finished resin with another compound having N atoms.

Description

~ - 2 - Z0~0789 SILO~E RESINS AND MEIHOD FOR MAKING THEM

This invention relates to siloxàne resins, and more specifically to certain silo~ane resins having mono-, tri-and tetra- functional units, hereinafter referred to as MTQ
resins. The invention also relates to a method for making these resins.
Organosiloxane resins having mono-, tri- and tetra-functional siloxane units are known and have been described for example in British Patent Specifications 7G6 719, 783 867 and 1 359 024. The ~unctionality of the siloxane groups refers to the number of silicon bonds which are formed or formable through silicon-oxygen bonds. In the first of t~ese specifications siloxane resins are prepared by reacting one or more silanes and/or one or more siloxanes with a silica hydrosol. Most of these resins are solid but so~e o~ the resulting materials described are liquid copolymers. In Examples 7 and 8 resins are described which are viscous li~uids being a copolymer of trimethylsilo~ane, monophenylsiloxane and SiO2 units and of trinlethylsiloxane, monostearylsiloxane and SiO2 units respectively. In the second of these specifications, the resins are described as finely divided solid organosilicon compounds which are used as fillers for optically clear organopolysiloxane elastomer compositions. They are manufactured by preparing a silica co-hydrogel from e.g.
~5 sodium silica~e ano a monoorganosiloxane salt, and reacting the co-hydro~el with a siloxane in an acidic medium. The last of the specifications ~entioned above provides profoamers which are copoly~lers consisting of R3SiO~ units, RSiG~ units and SiG2 units wherein R is an alkyl radical, a monocyclic aryl hydrocarbon radical, an alkaryl radical or an aralkyl radical, the ratio of monofunctional units to the total of tri- and tetra~unctional units combined is from 0.6/1 to 1.5/1 and the ratio of said trifunctional units to said tetrafunctional units is from 0.05/1 to 1/1.
All exemplified compounds are so]uble in xylene. Prepar-ation methods described in this specification include thecohydrolysis of a mixture of R3SiX, RSiX3 and SiX4 wherein ~ is as described above and X is a hydrolysable group, halogen being the only one disclosed; addition of a blend of R3SiX and RSiX3 to a stabilised hydrosol, and the addition of a solution of R3SiX to a stabilised hydrosol of silica and methylsiliconic acid. In U.S. Patent Specifica-tion 3 772 247 organopolysiloxane MTQ resins are described, e.g. in Examples 4, 5 and 6. The resins are described as brittle solids. The method of ~aking them is as described in G.B. 706 719. U.S. 3 772 247, however, also mentions as alternative methods the cohydrolysis described in G.B.
1 359 024 and the hydrolysis of a solvent solution of a triorganoalkoxysilane, a trialkoxysila,ne and a tetraalkoxy-silane. The latter two methods are not exernplified.
The resins described above are mainly solid resins at room temperature. There re~lains a need for resins which are liquid at temperatures around and slightly above ambient temperat~res, especially resins which have groups attached to thern which are able to react further or give a specific functionality to the resin. Such groups will be further referre~ to in this specification as reactive groups and include e.g. SiH, alkenyl, amino, thio, phosphate, ketone, acid and alcohol groups.
We have now found that novel ~TQ resins, which are liquid at 50~C and have a reactive group attached to them can be prepared.
Accordin,g to the present invention there are provided organosiloxa,ne resins which a,re liquid at 50~C at a pressure of lG Pa and have the general formula [MXTyQz]n, wherein M denotes a monofunctional siloxane unit of the formula R'aR3 aSiO~ wherein a has a value of from 0 to 3, T
denotes a trifunctional silox.ane unit of the general formula R"SiC~ and ~ denotes a tetrafunctional unit of the gen.eral formula SiO4/~, wherein R represents a saturated aliphatic hydrocarbon or an. aromatic hydrocarbon group, R' ~enotes hydrogenS an olefinically or acetylenically unsatu-rated hydrocarbon substituent, ~ substituted hydrocarbon or G an organic substituent linked to silicon via a silicon-carbon bond and baving O and/or N, S or P atoms present, R"
denotes a group R or a group R', there being at least one group R' per organosiloxane resin molecule, n has an average value o~ from 4 to 14 and x, y and z have values such that _ + ~ is not less than z and not more than 2z and_ that x/y has a value of from 2/1 to 9/1.
In the ~TQ resins of the invention each R group may independently be an alkyl, aralkyl, alkaryl or aryl group, e.g. propyl, butyl, hexyl or phenyl. Preferably, ho~ever, substantially all R groups are lower alkyl groups, most preferably methyl groups. The R' group, or reactive group, is selected fro~ the group including hydrogen, a hydro-carbon group which is ole~inically or acetylenically unsaturated, for example alkenyl, e.g. vinyl, allyl and hexenyl or alkynyl, e.g. ethynyl and propargyl and substi-tuted hydrocarbon, e.g. chloropropyl and trifluoropropyl.
R' may also be an organic substituent linked to silicon via a silicon-carbon bond and having O, N, ~ or P atoms in the substituent, e.g. those having --COH groups present, e.g.
-(CH2)3OH, (CH2)2(OCH2CH2)8CH and -CH2-C(CH3)-CH2OH, th.ose having acrylic groups presentS e.g. methacryloxypropyl and acryloxypropyl, those having aldehyde, ketone or acid groups present, those having thio groups present, e.g.

-_ 5 _ ~Q ~7~ ~

mercaptopropyl, those with sulfonic acid groups present, those with phosphonic acid groups present and those having amino, amido, amine oxide, ammonium, imide or imine oxide groups present. Preferably R' is hydrogen, an alkenyl or substituted alkyl group or an organic group having an acrylic, amino or thio group present. R" may be R if a has a value which is not 0. This means that the resin must have at least one group as defined for R' present per mole-cule. It is however preferred that a has a value of 0, and therefore R" denotes a group R'.
The liquid state o~ the resins of the invention at 50~C at a prèssure of 105 Pa arises from the above specified proportions and number of the different siloxane units. It is believed to be determined at least to some extent by the structure of the resin molecules. The appli-cant believes, but does not wish to be bound by this, that the structure of the resins o~ this invention is base~ on a core of Q units, which is surrounded by M and T units, thus differing from a more open structure of solid MTQ resins.
The exact molecular weight is determined by the desired proportions of the siloxane units of the resin. The value of _ + y has to be not less than z and not more than 2z._ Resins wherein the value of x + y is lower than z are solid materials, o~ten having an open structure and having a largely superior molecular weight than the resins of this invention, while values above 2z tend to give a material which has a very low molecular weight, and are believed to yield resins which do not have the desired structure. The ratio of x/y has a value of from 2/1 to 9/1. Preferably this ratio is in the range 3/1 to 5/1. The averàge value of _ is from 4 to 14. Values below about 4 are usually only obtained when resins are produced wherein the x + y is larger than 2z, while values above about 14 tend to yield solid resins.

'. ~
, - 6 - ~ 7 ~ ~

The liquid resins of the invention are very useful as fillers in elastomer-forming compositions, as materials providing a coating or as precursors for further reaction with other compounds.
Resins of the invention may be prepared by reacting together tetrafunctional alkoxysilanes, trifunctional silanes and monofunctional silanes or disiloxanes in an ~acidic aqueous medium.
According to another aspect of the present invention there is provided a method for making organosiloxane resins which are liquid at 50~C at a pressure of 105 Pa and have the general formula [MXTyQz]n, wherein M denotes a mono-functional siloxane unit of the forn~ula R'aR3 aSiO~ wherein a has a value of from O to 3, T denotes a trifunctional siloxane unit of the general formula R"SiO~ and Q denotes a tetrafunctional unit of the general formula SiO4/2, wherein R represents a saturated aliphatic hydrocarbon or aromatic hydrocarbon group, R' denotes hydrogen, an olefinically or acetylenically unsaturated hydrocarbon substituent, a substituted hydrocarbon or an organic substituent linked to silicon via a silicon-carbon bond and having O and/or N, P or S atoms present, R" denotes a group R or R', there being at least one group R' per organosi-loxane resin molecule, n has an average value of from 4 to 14 and x, y and z have values such that x + ~ is not less than z and not more than 2z and that the ratio of x over has a value of from 2/1 to 9/1, which comprises (I) adding together z molar parts of (A) a silane of the general formula SiZ4, ~ molar parts of (B) a silane of the general formula R SiY3 and either x molar parts of (C) a silane of R aR3_aSiX or x/2 molar parts of (C') a disiloxane of the formul3a (R aR3_aSi)2 medium, wherein R and R respectively denote R" and R' ,~

7 ~ ~ .

except for the organic substituent having N atomsS X
denotes a halogen or alkoxy group, Y denotes X or a group of the general formula -O~iR3 and Z denotes an alkoxy group provided that Component (A) is not added to the aqueous medium prior to Components (B) and (C) or C'), (II) allowing Components (A), (B) and (C) or (C') to react together in said aqueous medium, the medium having a pH
below 7, and (III) optionally further reacting the finished resin with another compound having N atoms. With the lC expression "molar parts" as used herein is meant that the components are aQded in such amounts that their molar ratio corresponds to the ratio of the number of M, T and Q units present iII the organosiloxane ~TQ resin molecule. In other words adding z molar parts of (A), y molar parts of (B) and x molar parts o~ (G) means that the molar ratio of (A)/(B)/(C) in the amounts added is e~ual to the ratio of z /y/x .
In the method of the invention there is used as Component (A) a silane of the formula SiZ4, wherein each Z
2G independently den,otes any alkoxy group, preferably a lower alkoxy group, most preferably having 2 to 4 carbon atoms, e.g. ethoxy and n-propoxy groups. Most preferred is tetra-ethoxy silane. These silanes, also called orthosilicates, are well known in the art and are commercially available materials. Preferred Components (A) include tetraethyl-orthosilicate (tetraethoxysilane), n-propylorthosilicate (tetrapropoxysilane) and tetr3butylorthosilicate (tetrabutoxysilane).
Component (B) is a trifunctional silane having three Y groups linked to the silicon atom and one group R2. R2 is as defined above and includes such groups as described for R" above, apart form the N containing organic substi-tuents. Preferred are those compounds where R2 is .~

7 ~ ~

hydrogen, alkenyl or substituted alkyl group or an organic group having an acrylic or thio group present. The gro-up Y
iTl Component (B) is alkoxy, preferably methoxy or ethoxy, a halogen, preferably a chlorine atom or a group of the formula -OSiR3, wherein R is as defined above and is preferably a methyl group. Examples of Component (B) therefore includè methyltrimethoxy silane, triethoxysilane, vinyltrichloro silane, phenyltrimethoxy silane, allyltri-ethoxy silane, ~lethacryloxypropyl trichloro silane, mercaptopropyl triethoxy silane, y-chloropropyl trimethoxy silane, trifluoropropyl trichloro silane and vinyltris (trimethylsiloxy) silane.
Components (C) and (C') for use in the method of the invention are respectively monofunctional silanes and disi-loxanes. The non-functional silicon-bonded substituents may be an unsaturated aliphatic or an aromatic hydrocarbon group R, reactive groups described above as R or a mixture of R and R3 groups. It is, however, preferred that the value of a eq~als zero and all substituents are therefore R
~roups. Preferably all R groups are lower alkyl groups, most preferably methyl groups. ~ may be an alkoxy group or a halogen group, preferably methoxy, ethoxy or chlorine.
Examples of materials which may be used as Component (C) are trimethylchlorosilane, triphenylchlorosilane, trimethylmethoxysilane, dimethylchlorosilane, glycidoxy-propyldimethyl methoxysilane and phenyldimethylchloro-silane. It is preferred to use Component (C') which is most preferably hexamethyldisiloxane.
The method of the invention is carried out in an 3C aqueous medium, which has a pH below 7. The medium may either be ma~e acidic by the addition of an acid, prefer-ably a sronsted acid, most preferably hydrochloric acid, or it may be made acidic due to the hydrolysis of some '' ~

a,,w of the components used in the method of the invention. ~he ]atter will happen e.g. if Y and/or ~ in Components (B) and (G) are chlorine atoms. In the presence of water, these components will hydrolyse and form HCl in the medium. If X
in Component (C) and Y in Component (B) is e.g. a chlorine atom, no acidification of the mediu~l may be required. Even if X in Component (C) would be e.g. a methoxy group suffi-cient acidification may take place by adding Component (B) if Y is a chlorine atom. However, additional acid is preferably added. When Component (C') is used, it is important to acidify the medium with an acid. If X and Y
of Components (B) and (C) are both chlorine atoms, it is possible to add Component (A) at the same time as (B) and (C) to the reaction mixture.
In stage (I) of the method of the invention, it is important that Component (A) is not added to the aqueous medium before Components (B), (C) or (C'). Component (A) may be added simultaneously with or subsequently to either or both of Components (B) and (C) or (C'). It is preferred ~G to disperse the Component (C) or (C') in the aqueous medium, before a mixture of Components (A) and (B) is gradually added. This method encourages the formation of the resins of the invention in such way that they have the correct structure to be liquid. ~owever, Component (B) may be added to the dispersion of Component (C) or (C') prior to the addition of Component (A). The addition of Component (A) prior to either or both of Components (B) and (C) or (C') would result in a resin which has a structure which favours the ~ormation of solids. Unless both X and Y
are haloger] atoms it is preferred that Component (A) is added subse~uently to the addition of either or both of Components (B) and (C) or (C').

~.
J
7 ~ ~ -The reaction in stage (II) of the method of the invention between components (A), (B) and (C) occurs as a result of the hydrolysis of the components and the subse-quent condensation of the thus formed silanol groups in the acidic medium according to the known reaction --SiOH + HOSi-- -----> -Si-O-Si- + H2O.
However, in view of the presence of Component (A), which upon hydrolysis forms a highly reactive compound of the formula Si(OH)4, it is recommended to add an alcohol in order to reduce the hydrolysis rate of Component (A), thus reducing the danger of premature condensation o~ the components and the possible formation of gel particles.
Suitable alcohols for this purpose include ethanol and isopropanol, the choice of alcohol being preferably the corresponding alcohol of the alkoxy group present as substituent Z. Preferably ethanol is used in combination with as preferred Component (A) tetraethoxysilane. The reaction between the components is preferably accelerated by reacting them at an elevated temperature, preferably around the re~lux temperature of the dispersion, e.g. 50 to 75~C.
In order to make a resin where R' is an organic substituent having N atoms, in step (III) of the method of the invention, a resin which is the reaction product of stages (I) and (II) of the method of this invention, where such resin has Si-H groups, may be further reacted with a compound having olefinic unsaturation as well as N atoms, e.g. as amino groups, e.g. allylamine, in the presence of a catalyst which catalyses the hydrosilylation reaction, e.g. a Pt compound or complex. Step 3 ~ (III) of the method is recommended as the amino groups would not be stable in the aqueous acidic medium in which the steps (I) and (II) of the method of the invention are carried out.

The resins produced by the method are recovered by standard methods, for example phase separation, washing, solvent extractiorl, distillation and drying. Step (III) is preferably only carried out after the resin of step (II) has been suitably recovered.
Making resins by the method of the invention allows one to ~ake them in a very reproducible way, and to obtain resins which have a comparatively narrow range of ~olecular weight. This was not possible using methods of the prior art.
There now follow a nu~ber of examples which illustrate the invention, in which Me denotes a methyl group, Ph a phenyl group and Vi a vinyl group and in which all parts and percentages are expressed by weight unless otherwise stated.
Example 1 To a flask ~itted with agitator an~ condenser 40g of concentrated hydrochloric acid were charged together with 30g of ethanol (95% v/v) and 60g of distilled water. The flask was kept under a nitrogen blanket and 113.4g (0.7 mole) of hexamethyldisiloxane was added. The mixture was heated to 50~C for 20 minutes, at which ti~e a mixture of 20~.4g (1 mole) of tetraethoxysilane and 104.6g (0.4 mole) of methacryloxypropyl trichlorosilane was added slowly over a period of 90 ~inutes. During the addition the temperature in the mixture rose to 68~C. When all the ingredients were added, the mixture was maintairled between 64 to 69~C for ar-~ extra hour. The organosiloxane resin was separated when the mixture was cooled. It was washed with distilled water and dried over MgSO4. After ~iltration the ixture was stripped of volatile components at 100~C and a pressure of 2 mbar. A pale straw coloured liquor was obtained, which had a viscosity at 25~C of 1059.7 mm2/s and Z0~0789 consisted of units of the formula SiO4/2, Me3SiO~ and CH2=C(Me)OCO(CH2)3SiO~ When repeating the procedure twice, materials having a viscosity of 1091 and 714.9mm2/s were obtained respectively.
Example 2 To a flask fitted with agitator and condenser 20g of concentrated hydrochloric acid were charged together with 15g of ethanol (95% v/v) and 30g of distilled water. The flask was kept under a nitrogen blanket and 64.8g (0.4 mole) of hexamethyldisiloxane was added. The mixture was heated to 75~C at which point a gentle reflux was observed.
At this time a mixture of 104.2g (0.5 mole) of tetraethoxy-silane and 31.2g (0.2 mole) of vinyltrichlorosilane was added slowly over a period of about 180 minutes. During the addition the temperature in the mixture rose to 85~C.
When all the ingredients were added, the mixture was main-tained at 85~C for an extra two hours. The organosiloxane resin was separated when the mixture was cooled. It was washed with distilled water and then extracted with toluene. After another washing in distilled water, the resin containing phase was dried over NaHCO3/MgSO4. After filtration the mixture was stripped of volatile components at 130~C and a pressure of 2G mbar. A water white liquor was obtained, which had a viscosity at 25~C of 326.2 mm2/s.
The resin consisted of the units SiO4/2, Me3SiO~ and ViSiO~. When repeating the procedure material having a viscosity of- 292.7 mm2/s and 404.7 mm2/s were obtained.
The Vi content was respectively 4.7, 4.8 and 4.6%.
Example 3 The procedure of example 2 was repeated four times, except for the fact that no HCl was added. Materials with a viscosity of 175.7, 175.9, 155 and 148.7 mm2/s respec-tively were obtained, having a respective vinyl content of 5.38, 5.29, 5.41 and 5.37%.

7 ~

Example 4 The procedure of Example 2 was repeated twice, except that ViSiC13 was replaced by ViSi(OCH2CH3)3, which was added over a period of 2 hours. The resulting résin had a viscosity of 1077 and 901.8 mm2/s and a vinyl content of 4.54 and 4.56% respectively.
Example 5 The procedure of Example 2 was repeated 3 times, except that the amount of hexamethyldisiloxane was reduced to three quarters and the ViSiC13 was replaced by ViSi(OSiMe3)3. The resin obtained had a viscosity of 97, 114.8 and 104.4 mm2/s respectively and a vinyl content of 3.79, 3.73 and 3.71% respectively.
Example 6 To a flask fitted with agitator and condenser 120g of concentrated hydrochloric acid were charged together with 90g of ethanol (45~ v/v) and 180g of distilled water. The flask was kept under a nitrogen blanket and 340.2g (2.1 mole) of hexamethyldisiloxane was added. The mixture was heated to 70~C over 35 minutes, at which time a mixture of 624.9g (3 mole) of tetraethoxysilane and 199.8g (1.2 mole) of Cl(CH2)3Si(OCH3)3 was added slowly over a period of 140 minutes. During the addition the temperature in the mixture rose to 76~C, which was maintained for two hours.
The organosiloxane resin was separated when the mixture was cooled. It was washed with distilled water and dried over MgSO4. After filtration ~he mixture was stripped o~
volatile components at 130~C and a pressure of 24 mbar.
579.1g (85.7% yield) of a resin was obtained, which had a viscosity at 25~C of 2525.4 mm2/s and a molecular weight of 995.4. The resin consisted of units o~ the formula SiO4/2, Me3SiO~ and Cl(CH2)3SiO~. When repeating the procedure twice, materials having a viscosity of 2619 and 1553 mm2/s and a molecular weight o~ 949.49 and 954.77 respectively were obtained.
Example 7 To a flask fitted with agitator and condenser 20g of concentrated hydrochloric acid were charged together with 15g of ethanol (95% v/v) and 30g of distilled water. The flask was kept under a nitrogen blanket and 64.8g (0.4 mole) of hexamethyldisilo~ane was added. To the mixture was added at a temperature of 15~C a mixture of 104.2g (0.5 lG mole) of tetraethoxysilane and 27.1g (0.2 mole) of HSiC13 was added slowly over a period of 165 minutes. During the addition the temperature in the mixture rose to 30~C. The organosiloxane resin W2S separated, washed with distilled water and dried over ~gSO4. After filtration the ~ixture was stripped of volatile components at 100~C and a pressure of 2 mbar. A viscous liquor was obtained, which had a viscosity at 25~C of 1802.3 mm2/s and a SiH content of 2.59%. The resin consisted of units of the formula SiO4/2, ~e3SiO~ and HSiO~.

Claims

1. Organosiloxane resins which are liquid at 50°C at a pressure of 10 5 Pa and have the general formula [M x T y Q z]n, wherein M denotes a monofunctional siloxane unit of the formula R'aR3-aSiO1/2 wherein a has a value of from 0 to 3, T denotes a trifunctional siloxane unit of the general formula R"SiO3/2 and Q
denotes a tetrafunctional unit of the general formula SiO4/2, wherein R is selected from the group consisting of saturated aliphatic and aromatic hydrocarbon substituents, R' is selected from the group consisting of hydrogen, olefinically or acetylenically unsaturated hydrocarbon substituents, halogen substituted hydrocarbons, organic substituents linked to silicon via a silicon-carbon bond and having oxygen present, organic substituents linked to silicon via a silicon-carbon bond and having nitrogen present, organic substituents linked to silicon via a silicon-carbon bond and having sulphur present, organic substituents linked to silicon via a silicon-carbon bond and having oxygen and nitrogen present, organic substituents linked to a silicon via a silicon-carbon bond and having oxygen and sulphur present and organic substituents linked to silicon via a silicon-carbon bond and having oxygen and phosphorus present, R'' denotes a group R or a group R', there being at least one group R' per organosiloxane resin molecule, n has an average value of from 4 to 14 and x, y and z have values such that x + y is not less than z and not more than 2z and that the ratio of x to y has a value of from 2/1 to 9/1.

2. Organosiloxane resins according to Claim 1 wherein a is zero.

3. Organosiloxane resins according to Claim 1 wherein substantially all R groups are methyl groups.

4. Organosiloxane resins according to Claim 1 wherein R' is selected from the group consisting of hydrogen, alkenyl groups, substituted alkyl groups, organic substituents having an acrylic group present, organic substituents having an amino group present and organic substituents having a thio group present.

5. Organosiloxane resins according to Claim 1 wherein the ratio of x/y is from 3/1 to 5/1.

6. A method for making organosiloxane resins which are liquid at 50°C at a pressure of 10 5 Pa and have the general formula [M x T y Q z]n, wherein M denotes a monofunctional siloxane unit of the formula R'a R3-a SiO 1/2 wherein a has a value of from 0 to 3, T
denotes a trifunctional siloxane unit of the general formula R"SiO 3/2 and Q denotes a tetrafunctional unit of the general formula SiO 4/2, wherein R is selected from the group consisting of saturated aliphatic and aromatic hydrocarbon substituents, R' is selected from the group consisting of hydrogen, olefinically and acetylenically unsaturated hydrocarbon substituents, halogen substituted hydrocarbons, organic substituents linked to silicon via a silicon-carbon bond and having oxygen present, organic substituents linked to silicon via a silicon-carbon bond and having nitrogen present, organic substituents linked to silicon via a silicon-carbon bond and having sulphur present, organic substituents linked to silicon via a silicon-carbon bond and having oxygen and nitrogen present, organic substituents linked to a silicon via a silicon-carbon bond and having oxygen and sulphur present and organic substituents linked to silicon via a silicon-carbon bond and having oxygen and phosphorus present, R" denotes a group R or a group R', there being at least one group R' per organosiloxane resin molecule, n has an average value of from 4 to 14 and x, y and z have values such that x + y is not less than z and not more than 2z and that the ratio of x to y has a value of from 2/1 to 9/1, which comprises (I) adding together z molar parts of (A) a silane of the general formula SiZ4, y molar parts of (B) a silane of the general formula R2SiY3 and either x molar parts of (C) a silane of the formula R3aR3-aSiX or x/2 molar parts of (C') a disiloxane of the formula (R3aR3-aSi)2O in an aqueous medium, wherein R2 and R3 respectively denote R" and R' except for the organic substituent having N atoms, X is selected from the group consisting of halogen atoms and alkoxy groups, Y is selected from the group consisting of halogen atoms, alkoxy groups and groups of the general formula -OSiR3 and Z denotes an alkoxy group, (II) allowing Components (A), (B) and (C) or (C') to react together in said aqueous medium, the medium having a pH below 7, and (III) optionally further reacting the finished resin, where said finished resin has Si-H groups, with a compound having olefinic unsaturation and N atoms in the presence of a hydrosilylation catalyst.

7. A method according to Claim 6 wherein the aqueous medium is acidified by addition of a Brönsted acid.

8. A method according to Claim 7 wherein the acid is HCl.

9. A method according to Claim 6 wherein Component (A) is tetraethoxysilane.

10. A method according to Claim 6 wherein in Component (B) Y is selected from the group consisting of methoxy, chlorine and -Si(CH3)3.

11. A method according to Claim 6 wherein a in Component (C) or (C') is 0.

12. A method according to Claim 6 wherein substantially all R
groups in Component (C) and (C') are methyl groups.

13. A method according to Claim 6 wherein Component (C') is hexamethyldisiloxane.

14. A method according to Claim 6 wherein an alcohol is added to the aqueous medium.

15. A method according to Claim 14 wherein the alcohol is ethanol.

16. A method according to Claim 6 wherein in step (I) Component (C) or (C') is dispersed in the aqueous phase before a mixture of Components (A) and (B) is added gradually.

17. A method according to Claim 6 wherein step (II) is carried out at an elevated temperature.